Rethinking the role of invertebrate hosts in the life cycle of the amphibian chytridiomycosis pathogen

Abstract

The amphibian pathogen Batrachochytrium dendrobatidis (Bd) has recently emerged as a primary factor behind declining global amphibian populations. Much about the basic biology of the pathogen is unknown, however, such as its true ecological niche and life cycle. Here we evaluated invertebrates as infection models by inoculating host species that had previously been suggested to be parasitized in laboratory settings: crayfish (Procambarus alleni) and nematodes (Caenorhabditis elegans). We found neither negative effects on either host nor evidence of persistent infection despite using higher inoculum loads and more pathogen genotypes than tested in previous studies. In contrast, addition of Bd to C. elegans cultures had a slight positive effect on host growth. Bd DNA was detected on the carapace of 2/34 crayfish 7 weeks post-inoculation, suggesting some means of persistence in the mesocosm. These results question the role of invertebrates as alternative hosts of Bd and their ability to modulate disease dynamics.

Extreme drought, host density, sex, and bullfrogs influence fungal pathogen infection in a declining lotic amphibian

“…, but see Betancourt‐Roman et al. ), we expected the presence of these invasive species to positively influence Bd in the system. We also tested for effects of different biometric variables (i.e., length, stage, and sex; Table ) as these have been associated with Bd prevalence and load in amphibian populations (Kriger et al.…”

Virulence and Pathogenicity of Chytrid Fungi Causing Amphibian Extinctions

“…These environments are difficult or impossible to replicate in vitro, favoring the development of either alternative animal models or amphibian skin tissue explants. Nematode Caenorhabditis elegans models have yielded promising results, although the observed pathogenicity may be due to toxic chytrid products rather than active fungal infection (10,124). The most relevant models use vertebrates in which active infections are established.…”

Chytrid fungus infection in zebrafish demonstrates that the pathogen can parasitize non-amphibian vertebrate hosts

“…1e). The increasing number of studies that have now shown conflicting evidence for the importance (or otherwise) of various non-amphibian hosts in acting as reservoirs of Bd is intriguing891011. Therefore, the challenge that lies ahead is to more closely examine the biotic and abiotic factors that govern the ability of Bd to parasitize alternative hosts, and to understand their contribution to the dynamic nature of chytridiomycosis across various ecological settings.…”

“…The nematode Caenorhabditis elegans is thought to also be parasitized by Bd with attendant mortality, and the keratin-rich toenails of waterbirds may act as a transient substrate for Bd 910. However, more recent research finds no evidence for roles of non-vertebrate hosts in sustaining infections11. An unexamined factor that may confound all of these studies is whether commensal bacteria either interact synergistically with Bd to exacerbate infection through dysbiosis, or rather protect against infection through the production of antimicrobial compounds12.…”